1. Field of the Invention
The present invention relates to a television device, and more particularly, to a screen detecting system of a wide screen television for detecting blank top and bottom areas of a video screen so that they can be eliminated by the wide screen television.
2. Description of the Prior Art
When wide screen televisions of aspect ratio 16:9 become more and more popular, compatibility problem for displaying the conventional 4:3 video frame of the NTSC system over a 16:9 display screen are commonly realized by many wide screen television vendors. Please refer to FIGS. 1A to 1C. FIG. 1A shows a conventional 4:3 video frame 10. Frame 10 is divided into three areas, a central area 11 of aspect ratio 16:9 for displaying 16:9 movies, a top area 12 and a bottom area 13 for displaying messages or logo occasionally. Such arrangement is commonly seen in cable television channels for displaying 16:9 movies in a 4:3 display screen. Inside the central area 11 a round circle 14 is displayed. FIG. 1B shows a 16:9 video frame 15 generated by using one prior art method. Frame 15 is generated by enlarging the video frame 10 horizontally. All the areas 11 to 13 are kept but the round circle 14 becomes an ellipse. FIG. 1C shows another 16:9 video frame 16 generated by the other prior art method which eliminates both the top and bottom areas 12 and 13 of the frame 10 and keeps only the central area 11. This method allows a true-copy display of the central area in exactly 16:9 aspect ratio but anything displayed in the top area 12 or bottom area 13 will totally be eliminated. Besides, if the video frame 10 displays a 4:3 image instead of a 16:9 movie, the image displayed on the top and bottom areas 12 and 13 will also be eliminated.